--- ac.scm.orig	2009-08-04 21:04:24.000000000 +0200
   +++ ac.scm	2009-08-04 21:21:33.000000000 +0200
   @@ -27,6 +27,7 @@
            ((eq? (xcar s) 'if) (ac-if (cdr s) env))
            ((eq? (xcar s) 'fn) (ac-fn (cadr s) (cddr s) env))
            ((eq? (xcar s) 'assign) (ac-set (cdr s) env))
   +        ((eq? (xcar s) 'defined) ac-defined)  ; to be called later in 'ac-mac-call
            ; the next three clauses could be removed without changing semantics
            ; ... except that they work for macros (so prob should do this for
            ; every elt of s, not just the car)
   @@ -254,6 +255,14 @@
                     ,(ac (cadr args) env)
                     ,(ac-if (cddr args) env)))))
 
   +(define (ac-defined x env)  ; called only via macro
   +  (if (pair? x)
   +      (and (ac-defined (car x) env)
   +	       (ac-defined (cdr x) env))
   +      (or (literal? x)
   +	      (lex? x env)
   +	      (bound? x))))
   +
   (define (ac-dbname! name env)
     (if (symbol? name)
         (cons (list name) env)
   @@ -462,8 +471,9 @@
 
   (define (ac-mac-call m args env)
      (let ((x1 (apply m (map ac-niltree args))))
   -    (let ((x2 (ac (ac-denil x1) env)))
   -      x2)))
   +    (if (procedure? x1)  ; 'defined call
   +	  (x1 args env)
   +	  (ac (ac-denil x1) env))))
  
    ; returns #f or the macro function